Digital data to be transmitted on a packet communications network can be characterized quite accurately by a very few statistical parameters. These parameters are normally used to determine if new traffic can be added to the transmission links of the network. These parameters, which together form a vector representation of the source traffic, could, for example, include the mean and variance of the bit rate and the effective bandwidth for the traffic. In the U.S. Pat. No. 5,289,462, issued Feb. 22, 1994, there is disclosed a traffic control system for packet communications networks utilizing an easily constructed and readily updated traffic load vector for representing the existing traffic load on each link of the network. A computationally efficient algorithm for updating these traffic load vectors is also disclosed which allows such updating in real time as connections are added to or removed from the network. In particular, each connection on the network is represented by a vector. The sum of all of the individual vectors representing all of the connections on a transmission link represents the total traffic on that transmission link. Each request for a connection or a disconnection is accompanied by a connection vector which can merely be added to or subtracted from the link load vector. New traffic is admitted to a transmission link only if sufficient capacity remains to carry that new traffic. All traffic seeking access to the network is assumed to have a single priority class, where priority class implies a particular guaranteed level of data loss probability.
In order to ensure that the traffic offered by each input connection remains consistent with the originally assumed statistical vector for that traffic, a so-called "leaky bucket" mechanism is provided to control the access of traffic to the network at the access point. Such a leaky bucket mechanism is transparent to the traffic so long as that traffic remains within the originally assumed statistical traffic parameters. If the incoming traffic exceeds these assumed values, the leaky bucket mechanism controls admission of the traffic to the network so as to enforce the original assumptions (until a new set of assumptions can be negotiated). One type of leaky bucket mechanism is described in the co-pending application Ser. No. 07/943,097, filed Sep. 10, 1992, now U.S. Pat. No. 5,511,513, and assigned to applicants' assignee.
Many types of digital traffic require two or more classes of traffic priorities for proper operation. For example, K. Lindberger discusses such a system in "Analytical Methods for Traffic Problems with Statistical Multiplexing on ATM Networks," Proceedings of the 13th International Teletraffic Congress, 1991. Multimedia traffic, in general, has the property that a single data source produces multiple data streams having different priority classes. Real time video data, for example, requires a much higher priority class than does the audio signal accompanying the video traffic. The traffic management system of the afore-mentioned patent application Ser. No. 07/943,097, now U.S. Pat. No. 5,311,513, unfortunately, is capable of handling only one priority class of traffic, and hence is unsuitable for multiple priority class traffic.